1. Field of the Invention
The present invention relates to methods for evaluating and manufacturing rubber and a method for manufacturing a joint seal used for an inkjet printer (hereinafter referred to as “inkjet-printer joint seal”).
2. Description of the Related Art
The degree of crosslinking of rubber is an important factor in determining rubber properties and is essential for designing and inspecting a rubber product. In general, measuring the degree of rubber crosslinking is often performed by a swelling test. However, since evaluating the degree of crosslinking by the swelling test is a method in which the swelling rate is measured by immersing a rubber sample in a solvent, several days are required for this evaluation, and hence the degree of crosslinking of rubber cannot be easily evaluated. In addition, when the amount of rubber which is used for the evaluation is small, the error of measurement is increased, and as a result, it becomes difficult to accurately obtain the degree of crosslinking.
In addition, as another method for measuring the degree of crosslinking of rubber, there may be mentioned a method in which the degree of crosslinking is obtained from a torque value of rubber which is measured using a curastometer. In this method, a non-vulcanized rubber is used as a sample, a vulcanizing curve of this non-vulcanized rubber is formed in which the horizontal axis indicates the time and the vertical axis indicates the torque, and the degree of crosslinking of rubber is evaluated using this vulcanizing curve. However, since being required to have a predetermined size or more and a specific shape, the test piece used for this curastometer evaluation is different from an actual product in size and in shape. Hence, it is difficult to determine accurate crosslinking conditions for an actual product from the measurement using a curastometer. In addition, since the above method cannot be applied to a crosslinked rubber, the degree of crosslinking of an actual rubber product cannot be evaluated.
As still another method for evaluating the degree of crosslinking of rubber, there may be mentioned a method in which the degree of crosslinking of rubber is evaluated by measuring a relaxation time by solid NMR (nuclear magnetic resonance) (see Japanese Patent Laid-Open Nos. 8-122284 and 2002-71595). However, by the measurement method using solid NMR, measurement is performed at a high speed, such as several tens of thousands rpm. Hence, in order to prevent a spinner (rotary tube) which contains a sample from being eccentrically rotated, it is necessary to uniformly fill the sample in the spinner. Accordingly, since it is difficult to measure a rubber product itself, pretreatment for the measurement is necessarily performed, such that a rubber sample is cut into a shape so as to be inconformity with the inside shape of the spinner or is ground into a powder. Furthermore, information thus obtained is average information of an entire sample, and when the degree of crosslinking of rubber varies from part to part, the deviation thereof cannot be evaluated.